This proposal is a continuation of the previously awarded grant by the National Cancer Institute dealing with molecular and electronic structure studies of a series of compounds which are of biological interest by electron diffraction and molecular quantum mechanical method. Various N-oxides as well as adenine-1-oxide, purine-N-oxide, and 6-methyl-purine-1-oxide have been chosen for investigation. The first part of this project, the development and revision of various computational programs for electron diffraction analysis and quantum mechanical calculations, has been completed. We are continuing the second part of this project, the investigation of the molecular and electronic structure of the proposed heterocyclic N-oxides. The parent compound of the N-oxide, pyridine-N-oxide has been completed and reported. Other substituted pyridine-N-oxides, such as 4-chloro-, 4-methyl, and 4-nitro-pyridine-N-oxides are presently under investigation. In order to understand the chemistry of purines and N-oxides, their structural and electronic information deem necessary, since none of the above mentioned structures has been reported. The constituents of pyridine-pyrazoles which are being studied in fighting against cancer are also under investigation. Further structural and quantum mechanical studies will aid in understanding the chemical reactivities and biological activities.